WASHINGTON — The U.S. State Department acknowledged Thursday it could have acted sooner to designate Nigeria’s Boko Haram a foreign terrorist organization, even though the Nigerian government and many Africa experts opposed the move when it was first considered two years ago.

The acknowledgment — accompanied by a caveat that it is impossible to say if an earlier designation would have had a significant impact on the group — came amid Republican criticism of former Secretary of State Hillary Rodham Clinton’s decision not to take the step in 2012. And it was made as senior U.S. officials declared to Congress that freeing the schoolgirls abducted by the radical Islamist group last month has become one of the Obama administration’s top priorities.

As the 276 girls entered a second month in captivity that has sparked global outrage, senior officials from the State Department, the Pentagon and the U.S. Agency for International Development told a Senate Foreign Relations subcommittee that the U.S. is committed to assisting Nigeria in combating the al-Qaida-linked Boko Haram as it expands its reach and builds capacity for more sophisticated and deadlier terror attacks.

At the same time, though, the officials lamented limitations on U.S. cooperation with the Nigerian military due to its poor human rights record. And they expressed concern about the Nigerian government’s commitment to fight the group and the ability of its army to do so.

“In general, Nigeria has failed to mount an effective campaign against Boko Haram,” said Alice Friend, the Defense Department’s principal director for Africa. “In the face of a new and more sophisticated threat than it has faced before, its security forces have been slow to adapt with new strategies, new doctrines and new tactics.”

Robert Jackson, a State Department specialist on Africa, told the panel that Nigerian objections to the State Department formally listing Boko Haram a “foreign terrorist organization” in 2012 were a main reason Clinton chose not to make that designation, which would have imposed sanctions.

At the time, some U.S. agencies, including intelligence services and the Justice Department, were pushing for the designation, saying the group met the strict criteria and was becoming a growing threat, not only to Nigerians but to U.S. interests in west Africa.

The Nigerian government, however, argued that such a designation could give undeserved visibility and credibility to what was then a largely localized insurgency. A group of leading Africa scholars weighed in, saying the designation might hurt the Nigerian government’s attempts to blunt the group’s influence by addressing poverty and promoting educational, health and infrastructure development.

After what Jackson called a “healthy debate,” Clinton opted to blacklist Boko Haram’s top three commanders as individual terrorists instead of designating the entire group.

It was not until last year, under current Secretary of State John Kerry, that the State Department listed Boko Haram as a terrorist organization. The administration has also offered a reward of up to $7 million for information leading to the capture of its leader.

Asked by Sen. Marco Rubio, a Republican, if that had been a mistake to wait, Jackson said the U.S. might act more quickly and be less deferential to foreign governments’ desires in the future.

“In retrospect, we might have done it earlier,” he said, adding: “I think the important thing is that we have done it and that we’ve offered a reward for the leadership of Boko Haram’s location.

“I think, senator, that there is definitely a lesson here,” Jackson told Rubio, “and I think that we will be quicker to act to make designations based on our own assessments earlier on based on this.”

The 2012 debate was rekindled last week after Clinton, a potential 2016 presidential candidate, joined the international outcry over the mass abduction of the girls. Clinton expressed solidarity with the kidnapped girls on May 4, tweeting that “access to education is a basic right & an unconscionable reason to target innocent girls. We must stand up to terrorism.” She ended the tweet with the popular hashtag, “#BringBackOurGirls.”

Republicans pounced, saying Clinton should have done more as secretary of state to prevent terrorism from wielding clout in the African nation.

America Rising, a pro-Republican super political action committee that has harnessed anti-Clinton energy in anticipation of a presidential run, seized on the matter. And Sharon Day, a co-chair of the Republican National Committee, questioned why Clinton declined to designate the group as a foreign terrorist organization. “She has harsh words for Boko Haram now. Why didn’t she take swift action against Boko Haram when she had the ability to do something?” Day wrote.

Clinton has yet to address the matter in depth, but she told a philanthropic group last week that kidnapping is “an act of terrorism and it really merits the fullest response possible, first and foremost from the government of Nigeria.” She also accused the Nigerian government of being “somewhat derelict in its responsibility” to protect its people.